Water evaporates from water bodies and goes into the atmosphere. Air also becomes hot due to sunlight and starts rising up taking along with water vapour. As the air rises up, it expands and cools. This cooling of air causes water vapour in the air to condense. The process of condensation of water occurs, if some particles (like dust) act as the ‘nucleus’ for these drops to form around. None these small droplets grow and become big by more and more condensation of other droplets of water. These steps form the clouds.
